[TowerTalk] More input

[K3BU@aol.com]

In a message dated 3/29/2001 04:38:25 Eastern Standard Time, jirka@jimaz.cz 
writes:

> 
>  WE HAVE LOST during last 20 years more  than 40 tips on 10m. We have had
>  various designs, stepping, material... We have used plain elements, closed
>  tips, end of tips with some weight- screw... open tips, ropes inside, even
>  Copper stranded conductor in PVC (better experience compared to rope inside
>  since it is less susceptible to ice and is heavier than the ROPE).

...and others mentioned 10m element problems.

If the tips are being lost, this would indicate that tip is vibrating, the 
last piece of tubing would vibrate from the mounting point on, last clamp to 
the tip. (Rest of the element can contribute to "tuning" of the tips too.) 
The maximum amplitude would be at the end (tip) of the tip, this is where 
dampening will be most effective. 

I would try to put some sand (granules or similar consistence material) 
inside of tubing towards the tip, maybe one-third from the end, seal it with 
plugs and make sure that there is a room for sand to "jump" inside, I would 
say no more sand than about one-third of space (volume).

something like this:
(last third of the tip)
__________________________________
     |                                                  |
     |                                                  |
     |    .   .   .   .   .   .  .   .   .   .   .      |
     | :  :  :  :  :  :  :  :  :  :  :  :  :  :  :  :   | 
__________________________________

 plug             sand                          plug

The other alternative might to use type of little "flag" made out of tape, 
rope or soft wire attached to the tips. Flag's flapping in the wind would 
counteract the vibration of the element tip (different resonant frequency). 
They just have to be made to last.

Variation of this is to add little extra wind loads, something like ping-pong 
balls, this would add some extra wind load when windy, that would dampend the 
vibrations too. 

It is always easier (cheaper) to bring the antenna down and try to get rid of 
vibration (while it is still intact) as soon as they are observed, rather 
than after elements fall off. They eventually will, it is a matter of time 
(number of cycles) I CAN GUARANTEE that. :-(

I have not tried the above (my antennas behave :-) but my logic tells me that 
it should work (no software used :-). Also liquid would work, just make sure 
it doesn't freeze (use antifreeze like Slivovica, Becherovka, Vodka, etc.:-)

It is important to remember that we need to have a mass present at the 
critical point that has different resonant frequency than the offender or is 
completely "wild" and will "jump" at a different beat than the offender and 
break his rhythm when he (she, it) wants to vibrate.

Yuri, oK3BU